Fluid pressure regulators regulate the flow of fluid between a high pressure port and a low pressure port. Typically, regulators are preset to allow fluid to flow when pressure at a low pressure port drops below a predetermined upper limit.
One type of pre-set regulator is known as a piston-type regulator. This regulator typically comprises a valve body, a hollow stem piston and a spring. When fluid pressure at the low pressure port of the valve body drops below a pre-set minimum, a coil spring operating on the underside of the piston head lifts the piston operated stem valve off the high pressure inlet port to provide fluid flow between the inlet port and the outlet port. At the same time, some of the fluids flow up the hollow piston stem to be captured in the cylinder head between the head of the valve body and piston face. As pressure at the outlet port increases, so does back pressure in the cylinder forcing the piston down and the piston stem valve against the high pressure inlet port.
U.S. Pat. No. 4,226,257 (Trinkwalder, 1978) discloses a regulator similar in structure and operating similar to that set forth in the previous paragraph. In such a piston type regulator, the cut-off pressure between the high (inlet) port and low (outlet) port is a function of the resistance force provided by the spring engaging, at one end, the valve body and at a second end, the underside of the sliding piston. The stouter the spring, the higher the cut-off pressure, the weaker the spring, the lower the cut-off pressure.
Such regulators are preset and have a fixed cut-off pressure. Changing the cut-off pressure requires changing the spring to a stouter or weaker spring. These regulators are useful for many purposes. However, a need exists for a simple piston type fluid pressure regulator wherein the cut-off pressure is adjustable between an upper and a lower limit. For example, in the air conditioning business, one may wish to recharge the system with a fluid under, for example, 60 pounds of pressure per square inch and use the same regulator to charge a system with a fluid under, say, 100 pounds of pressure per square inch. Additionally, certain fluid pressure testing equipment presently requires a number of pre-set regulators in 20 to 40 foot intervals. Applicant's invention provides, however, in a unique piston type fluid regulator, the capability of providing in a single regulator a device capable of adjustably selecting a cut-off pressure.